This invention relates to a particle acceleration system. Prior art systems used for accelerating particles are described in the U.S. Pat. Nos. to Johnson et al, 3,739,634 and Johnson et al, 3,893,335. To provide high velocity particles, relatively long flow interaction paths are required. For some applications, space limitations prohibit the use of long flow interaction regions. In a conventional centrifugal accelerator, the particles are thrown toward the wall of the accelerator into the boundary layer where there is a momentum loss due to friction in the boundary layer adjacent the wall. Compensation for these losses has been provided by multiple acceleration nozzles. Large radius channels are required, however, to provide a long single pass interactor path.